Container for liquefied gases



United States Patent Inventors Robert G. Jackson Hornchurch, England; Gilbert Massac, Meudon, France Appl. No. 761,158 Filed Sept. 20, 1968 Patented Dec. 15, 1970 Assignee Conch Ocean Limited a Bahamian company Priority Oct. 12, 1967 France No. 124,248

CONTAINER FOR LIQUIFIED GASES 6 Claims, 12 Drawing Figs.

US. Cl. 220/15; 1 14/74 Int. Cl 865d 25/00 Field of Search 220/9A, 9A',10,15,63,9F;114/74A References Cited UNITED STATES PATENTS 2,892,564 6/1959 Morrison 220/15 11/1963 Tucker 220/10 3.150.795 9/1964 Schlumberger 220/9(A') 3,215,301 11/1965 Armstrong 220/9(A') 3,332,386 7/1967 Massac 220/15X 3,337,079 8/1967 Clarke et a]. 220/15 3,392,866 7/1968 Alleaume 220/15 3,399,800 9/1968 Gilles 220/15 3,406,858 10/1968 Jackson 220/9 FOREIGN PATENTS 1,5 29,205 5/1968 France 220/9(A') 1,110,366 4/1968 Great Britain 220/9(A') Primary Examiner--.loseph R. Leclair Assistant Examiner-James R. Garrett Attorney-Max L. Libman ABSTRACT: A membrane-type insulated, large-scale prismatic container for cryogenic liquids, such as are used in tankers, having load-bearing insulating walls backing up thin, flexible membrane walls which constitute the primary container. The membrane walls are attached at the corners to rigid angle-section anchoring members which are supported by the insulating walls, and which are sufficiently strong to transmit to the insulating walls, without appreciable deformation, all loads transmitted to them by the membrane walls.

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PATENTED DEC] 5 I976 SHEET 08 0F M Home y 1 container: roa'uoutrrsn eases BACKGROUND OF THE INVENTION This invention relates to containers for the storage or transport of liquids at temperatures greatly differing from ambient temperature. The invention, is primarily intended for containers for cryogenic liquids, such as liquefied gases at near atmospheric pressure. For convenience, reference .will be confined in the following to containers for cold liquids, for exam ple liquefied gases, such as liquefied natural gas. Such containers are used, for example, in marine tankers, for the transport of liquefied gases.

The invention is exclusively concerned with containers of the kind, known as integrated tank containers. comprising a housing of load-bearing thermal insulating lined with a primary barrier, against leakage of fluid, in the form of a thin and flexible fluidtight membrane tank of cold-resistant sheet material, eg metal, which is'not subject to cold embrittlement, and which is not self-supporting" but is supported, against internal loads due to hydrostatic pressure and inertia forces, by the surrounding solid insulation. The insulation lines, and is itself supported by, a'relatively rigid supporting shell, so that the insulation directly transmits to the supporting shell all the pressure exerted by the fluid upon the walls of the membranetank.

Containers as defined in the preceding paragraph will hereinafter be denoted containers of the kind specified".

The walls of the membrane tank of a container of the kind specified will, unless prevented by'external'means, contract substantially when contacted by the cold liquid. The invention is exclusively concerned with containers of the kind specified and of the type in which the membrane tank is held against overall dimensional change due to thermal stress so that the overall dimensions of the membranetank remain unchanged relative to the supporting shell and the membrane tank remains in contact with and supported by the insulation.

Containers as defined in the preceding paragraph will hereinafter be denoted containers of the type specified".

In a container of the type specified, the loads upon the means holding and anchoring the membrane tank against overall dimensional change may be considerable. There may be considerable loads due to thermal stresses. Moreover, where the container is mounted in the hold of a marine taker, at least some of the walls of the membrane tank are subject to stresses caused by ship strains-when the taker is at sea which also produce additional loads upon the means anchoring the membrane tank against overall dimensional change. Thus the means anchoring the membrane tank against overall dimensional change due to thermal stresses must be designed to withstand such additional loads. But, where the container is mounted in the hold of amarine tanker the means anchoring the membrane tank against overall dimensional change are preferably not directly connected to the hull of the tanker because this would interrupt the insulation and provide heat/cold bridges which would locally reduce the temperature of the hull with dangerous consequences. in in designing containers of the type specified it is necessary to ensure that the insulation is capable of withstanding the hydrostatic loads imposed upon it by the membrane tank and also, when mounted in a ship, the stresses caused by the ship's strains at sea. The insulation must also be substantially nondeformable when subjected to temperature change and there must be no heat/cold bridges therethrough. Moreover, the means anchoring the membrane tank against overall dimensional change must not prejudice the thermal insulating properties of the insulation. These requirements in practice present a number of problems.

Moreover, it is prudent, and is at present a statutory requirement. to provide in containers of the kind specified, a secondary barrier against the leakage of fluid should the pri-. mary barrier membrane tank fail. Such a secondary barrier may be in the form of a further membrane tank, e.g. of thin metal, enclosing the primary barrier membrane tank and supported by load-bearing insulation. In an alternative known construction the secondary barrier is constituted by the insulation supporting the primary barrier membrane tank, or is in the form of a nonmetallic, e.g. plywood, sheet incorporated in the insulation. As will be appreciated in this case it is even more important that the insulation shall be reliable and shall not be interrupted by heat/cold bridges which might also act as leakage points.

Various prior proposals have been made for the construc- I tion of containers of the type specified. In one proposal, the container has in identical primaryand secondary membrane tank barriers of thin sheet metal each supported by a surrounding wall of insulation. Each such wall consists of a framework supporting rigid hollow blocks containing granular insulation and free freely mounted one upon the other. The corners of each of the. primary and secondary membrane tank barriers are anchored by means extending from each corner through the insulation to the supporting shell. This arrangement has a number of disadvantages, amongst which is the fact that the two walls of insulation are constituted by free blocks which may move. That is to say the blocks of each wall of insulation may move so that their membrane tank supporting faces are no longer in alignment and do not provide a smooth surface so that the membranefiank may fracture. This could .be dangerous particularly'where, as is primarily the intention, the container is used in a ship. Another disadvantage is the interruption of the insulation by the comer anchoring means of the membrane tanks, which form heat/cold. bridges.

In another proposal, there is a single membrane tank primary barrier supported by a'solid wall of insulation, constituted by rigid wood panels or blocks which are each individually fixed to form a substantially continuous wall, so that their membrane tank supporting faces remain in a common plane and provide a permanently smooth supporting face for the membrane tank. The insulation itself constitutes or incorporates a nonmetallic secondary barrier and each block is substantially fluid-impermeable and the gaps between adjacent panels or blocks are filled with sealing material and closed by scabs connecting the panels so that the insulation remains a fuidtight secondary barrier notwithstanding contraction of the panel the panels. The anchoring means for the membrane tank are spaced at intervals on the insulation along and across the walls of the membrane tank in such a way that they support the loads of the membrane tank along each wall. A disadvantage of this arrangement is that the corners of the membrane tank may not be maintained rigid and may be liable to fail. in a further prior proposal, the membrane is held by means of angle-section anchoring members of rigid material extending along the corners of the membrane tank and secured to a rigid framework disposed within the insulation and secured to the rigid shell. This arrangement has the disadvantage that the accommodation of the framework additional to the insulation is more complicated and the fact that the framework is secured to the insulation actually in the corner of the latter vitiates against the requisite expansion and contraction of the insulation. v

An object of the present'invention is to overcome the disadvantages of the prior proposals and meet the above stated problems by the provision of a container of the type specified having an integrated structure in which the individual require ments of the insulation, the membrane tank and the anchoring means for the latter are suitably allied to one another.

A specific aim of the invention is to provide a marine tanker equipped with one or more containers, the membrane tank walls of which are at all times supported by the surrounding insulation and in which the membrane tank and particularly the comers thereof are less liable to deformation and fatigue failure.

SUMMARY OF THE INVENTION Broadly considered, the present invention provides a container of the kind and type specified in which the corners of the membrane tank are anchored to the corners of the insulation by means of rigid angle-section anchoring members extending externally along the corners of the membrane tank and secured to the corners of the insulation, whereby the corners of the membrane tank are rigidly anchored to the insulation and are held against any appreciable deformation.

More specifically, the invention provides a container of the kind and type specified in which: (a) the load-bearing thermal insulation is secured to the supporting shell against movement away from the shell and is such that when subjected to change in temperature it does not deform (except to a limited extent at the corners) so that it permanently provides a smooth supporting surface for the membrane tank; (b) the corners of the membrane tank are anchored to the corners of the insulation by means of rigid angle-section anchoring members extending externally along the comers of the membrane tank and secured to the corners of the insulation; and (c) at least the corners of the insulation are of materials of tensile and compressive strength sufficient to transmit to the shell the loads upon the anchoring members, whereby the corners of the membrane tank are rigidly anchored to the insulation and are held against any appreciable deformation.

The idea of the invention is that, instead of the anchoring members being connected with the supporting shell by means extending through and additional to the corners of the insulation, the anchoring members are merely connected to the corners of the insulation which are relied upon to transmit the loads to the supporting shell. In this manner the problems, presented by additional means extending-.through and interrupting and forming heat/cold bridges through the corners of the insulation, are avoided.

lt is to be clearly understood that the term corner" is used throughout this specification to mean the length of the junction formed by the edge portions of two adjoining walls, or portions of walls, either, of the membrane tank or of the insulation or of the complete container. The term wall" includes the top and bottom.

The integrated containers in accordance with the invention may be of any geometrical shape, They will usually be prismatic or parallelepipedic but may be of a more complex shape with plane walls or relatively inclined plane wall portion, for example, for fitting into the bottom of the inner hull of a tanker. The containers may also be stepped in the sidewalls or bottom or top walls so that the container is of progressively different cross-sectional sizes, for example for closely fitting within the forward or aft parts of a tanker. In any event, the membrane tanks will have corners formed at the junction of the edge portions of adjoining walls or portions of walls. Adjacent walls may form a dihedron with a junction in the form of a straight line or edge. However, the junction may be in the form of a curvilihear edge line. The angle of the dihedron may be substantially orthogonal or right but particularly in the case of a tank having relatively inclined wall portions, the angle may be of any value, for example, an obtuse or acute angle, depending upon the geometrical shape of the tank. Some of the corners in a tank of any geometrical shape may be in the form of inner comers or solid angles which are internal or entrant. However, the tanks, and particularly those in which the sidewalls and top or bottom walls are stepped or those having a narrow upper extension or trunk, have dihedral external corners which are salient or reentrant.

An important feature of the invention is that the angle section anchoring members are rigid enough to be substantially nondeformable and to render substantially invariable the angle of the corners of the membrane tank, that is to say the angle between the walls or portions thereof constituting the corners, thereby reducing the possibility of fracture of the corners of the membrane tank. Thus, although the members anchor the membrane tank against overall dimensional change due to thermal stress and are, for convenience, designated anchoring members throughout this specification, they also rigidly support and hold the corners of the membrane tank against any substantial change in the angle of the corner.

Another important feature of the invention is that the anchoring members are secured to the insulation at short distances from the line junction of the internal corners of the insulation so as not to interfere with the deformation of these corners under expansion and contraction of the insulation. Each limb of the angle-section anchoring member extends a short distance along the face of the insulation away from the line junction of the comer and is secured at a distance from the line junction, e.g. by means of bolts or screws, to rigid load-bearing insulation blocks, e.g. of hardwood, rigidly secured upon the face of the insulation in such manner, e.g. by adhesive, as not to prejudice the fluid-tightness of the insulation. That is to say the blocks extend or are distributed along each of the edge portions flanking the line junction constituting the corner of the insulation adjacent the corner of the membrane tank. Because the blocks supporting the two limbs of each anchoring member are' spaced at distances from the line junction of the corner along the adjacent walls of the insulation, there is a gap between the anchoring members and the corner of the insulation which accommodates the deformation of the latter.

A further feature of the inventionis that the tensile load in any wall of the membrane tank is taken partly by that wall of the insulation extending parallel to and associated with said wall of the tank, and partly by that wall of the insulation extending perpendicularly thereto. Part of the tensile load in any wall of the membrane tank is taken in shear through the wall.

of insulation supporting said wall of the tank to that wall of the shell extending parallel to said wall of the tank and which supports the insulation supporting said wall.

The membrane tank may be of any suitable cold-resistant flexible material, e.g. metal, which is not subject to cold embrittlement at the temperature of liquefied gases at atmospheric pressure. Throughout this specification the term metal" is intended to include alloys. The membrane tank may be of metal, e.g. stainless steel, or an aluminum alloy, which does not have an unduly low coefficient of thermal expansion but is formed with expansion formations, such as corrugations or dimples, in two directions providing excess metal to accommodate contraction. Alternatively, the membrane tank may be of metal, such as the 36 percent nickel steel known as lN- VAR, which has a very low coefficient of thermal expansion and which may or may not require to be provided with expansion formations.

The angle-section anchoring members may be of any appropriate metal, for example, stainless steel, an aluminum alloy, or lNVAR, of a suitable strength and thickness to provide the requisite rigidity. It is important that the material of the anchoring members shall be compatible, for example, in its coefficient of thermal expansion and in capability of welding, with the material of the membrane tank. Preferably, the same metal is used for both membrane and anchoring members although this is not essential providing that the metals can be welded to one another and have similar coefficients of expansion. in order to enhance the rigidity, each angle-section anchoring member may beprovided at intervals with external ribs or webs either formed integrally with the anchoring member or welded thereto.

lt is necessary to cater for the expansion and contraction of the anchoring members. Preferably this is achieved by separating each anchoring member extending along the length of a corner of the tank into a plurality of short members with gaps between the adjacent ends thereof. In this case, the gaps will be closed in fluidtight fashion by thin plates bridging and welded to adjacent members and preferably formed to accommodate contraction and expansion. Conveniently, these connecting plates are constituted by the corner pieces of the membrane tank itself. In this respect it is primarily the intention that the membrane tank shall have, disposed within the anchoring members comer pieces which form, with the walls, the complete fluidtight tank. In this case, in general, the

anchoring members do not form part of the membrane tank, although small portions of the members may form a seal.

As indicated above, the thermal insulation of the container of the invention must essentially form rigid load-bearing walls, of sufficient compressive strength to support against hydrostatic loads the walls of the membrane tank, and the loadbearing walls together form a complete structure which permanently remains fluidtight. Although any suitable material(s) which meets the criteria specified above, may be used, it is primarily the intention that the insulation shall be constituted by blocks or panels, e.g. of balsa wood, each individually secured to the supporting shell and the panels forming each wall are secured together to form a complete solid wall but in which some provision is made for limited deformation of the portions forming the corners of insulation. Preferably the insulation is of the form described in U.S. Pat. No. 3,1 12,043 in which there are gaps between adjacent blocks or panels, which are filled with sealing material and closed by scabs connecting the panels; Insulation of this form is of sufficient tensile and compressive strength to transmit to the supporting shell the loads upon the anchoring members. Alternatively insulation of this form may be utilized to form the corners of the insulation, where both compressive and tensile strength is required and some other thermal insulation material having only the requisite compressive'strength e.g. a foamed plastic material, may be used to form the main portions of the walls of the insulation.

It is primarily the intention that the insulation of the container shall constitute or incorporate a nonmetallic secondary barrier against the leakage of liquid.

DESCRIPTION OF THE FIGURES In order that the invention may be more clearly understood, specific constructional examples thereof will now I be described with reference to the accompanying drawings.

FIG. 1 is a diagrammatic transverse vertical cross-sectional view of a marine tanker showing a rectangular container comprising a single membrane tank mounted in a cargo hold of the tanker; in the left-hand part of this FIG. the relevant portion of the membrane tank is omitted.

FIG. 2 is a sectional plan view of one-half of the cargo hold shown in FIG. 1 showing two early stages in the construction of the container; the upper part of this FIG. shows one-quarter of the cargo hold with the ground stripsin positiomand the lower part of this FIG. shows another quarter of the cargo hold with the insulation panels and supporting hardwood blocks and intervening balsa blocks of the container mounted therein.

FIG. 3 is a sectional plan view, similar to FIG. 2, of the other half of the cargo hold showing the final stages in the construction of the container; the lower part of this FIG. shows onequarter of the cargo hold with the angle-section anchoring members of the container mounted in position and the upper part of this FIG. shows the relevant portion of the membrane tank in position.

FIG. 4 is a detail sectional plan view, on a larger scale, showing, inter alia, the angle-section anchoring members at an entrant dihedral angle between parts of adjoining walls and the bottom of the container of FIG. land a three-way' trihedral angle-section anchoring member at the junction therebetween and the associated portions of the membrane tank and the thermal insulation.

FIG. 5 is a fragmentary perspective view, with parts broken away, of the angle-section anchoring members at an entrant dihedral angle between a portion of a wall and the bottom of the container in FIG. I, the associated portions of the tank and of the thermal insulation.

FIG. 6 is a detail vertical cross-sectional view, on a larger scale, of the container of FIG. 1.

FIG. 7 is a detail sectional plan view on a larger scale through a three-way trihedral angle-section anchoring member and adjacent dihedral anchoring members and the associated thermal insulation material of the container of FIG. 1.

FIG. 8 is a detail cross-sectional view on a much larger scale, showing one method of securing the plates constituting the membrane tank.

FIG. 9 is a detail vertical cross-sectional view, on a large scale, showing the arrangement at a dihedral obtuse corner of another container having relatively inclined sidewall portions.

FIG. 10 is a general perspective view of another container having stepped sidewalls and both entrant and reentrant corners.

FIG. 11 is a detail sectional view similar to FIG. 6, showing the arrangement at a reentrant or salient corner of a container.

FIG. 12 is a general perspective view of a modified form of the angle-section anchoring members.

It is to be clearly understood that FIGS. 1, 2 and 3 are not to scale. That is to say the portions of the membrane tank, the anchoring members, the mounting blocks and the thermal insulation are all shown, for convenience of illustration, on a much larger scale than the double hull of the tanker.

FIG. 1 shows a cross section of a marine tanker for the transport of liquefied natural gas and having containers comprising thermally insulated cargo tanks supported in cargo holds and having the general configuration of said holds. The tanker is provided with an outer hull I and an inner hull 2. Deck plates are indicated at 3 and the transverse bulkheads defining the ends of the cargo hold are shown at 4 (FIGS. 2 and 3). The cargo holds serve as the relatively rigid supporting shell of each container. The cargo holds are each internally lined with walls of load-bearing thermal insulation indicated generally at 5 (FIG. 1). Disposed within the insulation in the cargo hold is a primary barrier membrane tank, indicated generally at 6, of thin flexible stainless steel sheet. Each wall of the load-bearing thermal insulation 5, comprises as described in the specification of U.S. Pat No. 3,112,043 a substantial layer of load-bearing thermal insulation, such as balsa wood, secured to timber ground strips 7 which together serve to provide a smooth surface for supporting the walls of the membrane tank and to transmit loads to the shell 2, or the plates 3 or bulkheads 4, as the case may be.

The layer of insulation is formed by panels 8 having a balsa wood core 9 and plywood faces 10 and 11'(FIG. 6), bonded to the core by a suitable adhesive. The plywood face 10 constitutes a secondary barrier.

As shown in FIG. 2, the timber ground strips 7 are attached at regular intervals to the rigid shell 2, plates 3 and bulkheads 4, for example, by means of threaded Nelson studs 7a (FIG. 6), so that the inner faces of the strips lie in a common plane. The spaces between the strips are filled with any suitable thermal insulation, e.g. glass fibre (not shown). The outer edge of each panel 8 contacts and is bonded to the inner surface of a ground strip 7; adjacent panels being bonded to a common strip so that they are interconnected in such a way that a fluid tight joint is formed. The panels are temporarily held in place during bonding by means of threaded Nelson studs (not shown) welded to the shell 2, plates 3 and bulkheads 4. These studs may or may not be permanently left in position.

The secondary barrier is designed to remain permanently fluidtight notwithstanding the tendency of the panels 8 to contract when subjected to low temperature. Thus, as described in U.S. Pat. No. 3,1 12,043, the edges of adjacent panels 8 are beveled so that there is a gap between adjacent panels, widening in the direction of the inner surface of the panels, which is filled with foamed plastic material 12 compressed to percent, or less than 90 percent, of its free volume. The gaps between adjacent panels 8 are closed at the outside by the ground strips and at the inside by scabs 13 (FIGS. 1 and 5) of plywood, overlapping and bonded to the panels at each side of the joint.

Thus, the panels 8 forming one wall are rigidly secured together by the strips and scabs to form a continuous loadbearing wall of high rigidity in which the panels are incapable of movement away from the rigid shell so that the inner faces remain in fixed positions relative to the supporting shell.

The gap at the corner between the panels 8 of the two walls forming a corner is filled with material 14 identical with material 12. A corner scab or cover 15 (FIGS. 6 and 7), preferably of plywood, is bonded to the adjacent panels and with a fillet 15a closes the gap between the panels. However, the scab or cover 15 permits limited relative movement and deformation of the panels forming the corner ofthe insulation.

The primary barrier 6 in this example is fabricated, as will be described in more detail below, from relatively thin and flexible sheets 16 of stainless steel forming the walls of the tank and connected together at the dihedral corners of the tank by sheet form corner pieces 17 of stainless steel and at the three-way trihedral corners by trihedral corner pieces 17' (FIGS. 3 and 6).

The sheets 16 constituting the walls of the tank are formed with expansion formations providing excess metal accommodating contraction when subjected to the cold temperature of the liquid. These formations are in the form of two sets of corrugations 16a, 16b (FIG. 4). In each set, the corrugations are of substantially identical cross-sectional size and extend in parallel-spaced relationship. The corrugations 160 are of greater cross-sectional size than those of the set 16b. The corrugations of one set intersect at right angles the corrugations of the other set so as generally to form a network of orthogonal pattern, the corrugations of which all project to the inner side of the tank.

The corners of the membrane tank 6 are anchored, so that it is held against overall dimensional change, by means of anglesection anchoring members indicated generally at 18 (FIG. 6), extending along the corners of the tank and to which the tank is welded. The anchoring members are constituted by relatively short members 19 of stainless steel extending in alignment with one another and at regularly spaced intervals along the length of the corner of the tank. The anchoring members are rigidly secured by means of bolts 20 (FIG. 4) to hardwood blocks 21, 22 in turn rigidly secured to the inner face of the insulation 5 in such manner, e.g. by adhesive, as not to prejudice the fluid-tightness of the insulation.

This arrangement will now be described in more detail, The hardwood blocks 21, 22 are shown most clearly in the lower portion of FIG. 2. A plurality of identical hardwood blocks 21 are spaced at regular intervals along the length of the edge portion of the bottom of the thermal insulation of the container, close to the adjacent sidewall. These blocks 21 are each of T-section in plan. The small stem of the T is located close to the edge of the bottom of the insulation and the wide bar of the T is spaced inwardly therefrom. Also secured, e.g. by adhesive, to the panels forming the bottom of the insulation, in the intervening spaces between the hardwood blocks 21, are small blocks 23 of balsa wood. It is to be noted that a balsa block covers the scab 13 of the insulation as shown in FIGS. 1, 2 and 3. As shown most clearly in FIG. 2, at the three way corner, e.g. the junction between the bottom wall and two adjacent sidewalls, a larger hardwood block 22 is provided. This block 22 may, in fact, be formed in one piece with the two flanking hardwood blocks 21.

As shown in FIGS. 4 and 5, there is an identical arrangement of hardwood blocks 21, 22 and intervening balsa blocks 23 extending along the marginal edge portion of each of the sidewalls adjacent the bottom wall and aligned with the blocks on the bottom. There is also an identical arrangement of blocks on the top wall of the insulation, as shown most clearly in FIG. 1, and along the upper marginal edge portions of the sidewalls adjacent the top wall.

The area defined between the blocks 21, 22, 23 of each wall of insulation is filled with balsa wood 24, secured, e.g. by adhesive to the panels 8 forming its bottom wall. Balsa wood 24 is of the same depth as the blocks and rebated to accommodate the scabs 13 so that its upper face is flush with the blocks and the balsa wood 24 constitutes, with the blocks, a further thickness of the insulation 5 and presents a permanently plane surface for supporting the membrane. Because all layers of the insulation, viz. strips 7, panels 8, balsa wood 24 and blocks 21, 22, 23 are all secured together and secured to the shell 2, 3, 4 against movement away from the shell the membrane 6 is permanently supported by said flat surface.

In FIGS. 18 the rigid angle-section anchoring members 19 have the shape of an entrant dihedral angle. Each member is provided adjacent, but spaced a short distance from, its opposite ends with two identical webs 19c (FIGS. 4 and 5) formed from thick flat stainless steel sheet and welded to the member to enhance its rigidity.

Each corner piece is mounted upon and secured to the stem portion of the T of one hardwood block upon each of the two wall flanking the corner. Thus, for example as clearly shown in FIG. 5, one limb 19a of each piece is rigidly secured by four stainless steel bolts 20 to a hardwood block 21 on the bottom wall of the insulation and the other limb 19b is rigidly secured by four stainless steel bolts 20 to an aligned hardwood block 21 on the adjacent sidewall of the insulation. The step of the T-shaped hardwood block is rebated so that the face of the limb of the anchoring member is flush with the remainder of the block.

Bolts 20 are engaged with captive nuts 25 disposed within small holes in blocks 21,22. As shown most clearly in FIGS. 2 and 4 there are gaps between the blocks 21 and 23 and corner blocks 22 for accommodating webs 19c. Aligned slots 26 (FIG. 7) may be formed in the bar of the T-shaped blocks 21 to facilitate mounting in position and possibly removal of the members 19. The edges of the walls of the membrane tank 6 are attached in fluidtight manner to the respective limbs 19a, 19b (FIG. 5) of the members 19, e.g. by welding for example by an arc-welded lap joint.

The corner pieces of the membrane tank are similar except for the pieces 17' at the three-way corner. Each is of short length and is formed with one corrugation or formation 17a connecting the aligned corrugations in the sheets forming the walls connected by the corner piece. The formations may be of different sizes or shapes for connecting corrugations of different sizes. Each piece is of somewhat greater length than members 19 and corner pieces 17 are mounted upon members 19 such that each corner piece 17 bridges two members 19 and covers the gap between adjacent members 19 with the corrugation extending above the gap between members 19.

Each corner piece 17 extends over a substantial proportion of the width of the limbs 19a, 19b of each member 19 and overlaps and is welded in sealing fashion to the edge portions of adjacent sheets 16 and at one end overlaps and is welded in sealing fashion to the adjacent piece 17. These overlapping portions are stepped corresponding to the thickness of the overlapped sheet.

As shown most clearly in FIGS. 1, 3 and 7, at each trihedral corner of the container a trihedral stainless steel anchoring member 19 is provided. This is of the same thickness as the members 19 but is of shorter length and is not provided with webs such as those on the dihedral corner members 19. Each limb is secured by four bolts 20 to the hardwood block 22 provided upon each of the three adjoining walls of insulation constituting the three-way corner. Thus, this anchoring member 19' is rigidly secured to the three walls. However, it is to be noted that there is a space S (FIG. 6) between the inner face of the panel 8 flanking the corner and the hardwood block 22 secured to the adjoining panel of the adjacent wall which permits contraction and expansion of the end portions of these panels at the three-way corner.

Mounted upon the trihedral anchoring member 19 is the trihedral membrane corner piece 17 (FIG. 6). This comprises three plane limbs not formed with corrugations and these limbs lie in facial contact with the inner surfaces of the trihedral member 19' and its edges are welded to the latter. The limbs of the membrane corner piece 17' are smaller than those of the member 19* and are overlapped by the edge portions of the adjacent dihedral membrane corner pieces 17, as

clearly shown in FIG. 6. There may be a small gap such as that indicated at X in FIG. 6 between the adjoining wall sheets 16 and the membrane corner pieces 17, 17' but this will be closed in fluidtight fashion by the underlying limb of the trihedral member 19.

Thus, the dihedral and trihedral supporting corner members are welded to the edges of the walls of the membrane and also to the corner pieces of the membrane and are rigidly connected to the membrane in such a manner as to withstand the high loads which will be encountered. The anchoring members are rigidly secured to the hardwood blocks which are, in turn, rigidly secured to the insulation but permitting deformation of the latter.

The bars of the T-shaped hardwood blocks 21, 22 support the first corrugations adjacent the edges of the membrane.

The sequence of steps in the construction of the container within the tanker is as shownin the various parts of FIGS. 2 and 3. Thus, the ground strips 7 are first secured to the inner hull 2, deck plates 3 and transverse bulkheads 4, as shown in the upper part of FIG. 2. The plywood-faced balsa panels 8 are now mounted in position and the gaps filled and enclosed by scabs. The blocks 21, 22 and 23 and the balsa layer 24 in the area defined between the blocks are all then mounted in position as shown in the lower part of FIG. 2. The dihedral and trihedral anchoring members 19, 19' are now mounted and secured in position upon the blocks 21, 23 as shown in the lower part of FIG. 3. The trihedral membrane corner pieces 17' are welded into position within the trihedral members 19'. The sheets 16 forming each wall of the membrane tank are then positioned upon the insulation material and the edges of adjacent sections welded together, as will be described below. The edges of the sheets forming the edges of each wall of the tank are then welded to the members 19. Finally the dihedral membrane corner pieces 17 are mounted in position and.

welded to one another and to the walls of the membrane tank, to complete the container as shown in the upper part of FIG. 3 and the right-hand part of FIG. 1.

Alternatively, each anchoring member may be secured to the two blocks 21', 22 as a subassembly and the blocks then secured to the corner panels 8; either when the latter are mounted in position or as a larger subassembly, i.e. before the corner panels are mounted in position.

The sheets 1'. forming each-wall of the membrane tank are located upon the insulation and welded to one another in any appropriate fashion and with the aid ofany suitable fixing arrangement. One example of such arrangement is found in FIGS. 4 and 8.

A plurality of such arrangements extends at spaced intervals across the walls of insulation, e.g. across the bottom (FIG. 4), adjacent the overlapping edges of the sheets 16 remote from the corners of the tank. Each arrangement comprises, let into hardwood in the insulation, a metal nut 27, preferably of stainless steel, secured by screw 28, (FIG. 8) underlying the edge of part of the sheet 16 which is formed with a hole in alignment with the nut 27 and is overlapped by the edge portion of an adjacent sheet 16. A nut 27 adjacent the edges of a wall will be located in block 21 (FIG. 4), but a nut 27 at a distance from the edge will be located in a hardwood block 29 let into the balsa wood 24 and secured by adhesive. The edge of the underlying sheet 16 is temporarily secured by a bolt (not shown) having a large head and engaged with nut 27. With the sheet temporarily secured and located upon the insulation the relevant edges of the sheet 16 are welded to the members 19 and adjacent sheets 16. Upon completion of this welding the indicated generally at 35, 36 defining a dihedral obtuse angle corner and the arrangement of the anchoring members at such corner. The portions 36 may form, for example, the chamfered sidewall portions adjoining the bottom of a container. The membrane 6 is again constructed from sheets 16 and corner pieces 17, 17'. However. in this case, in order that the corrugations in the wall of the membrane at the end walls 37 can be connected to the corrugations in the wall 36 parts of the marginal edge portions of the sheets 16 on the end wall are cut away and replaced by small plates 38 formed with elbow corrugations 380 which connect the corrugations in the wall 35'. The arrangement is identical with that at a dihedral rightangled corner, that is to say the insulation comprises panels 8, the gaps between which are covered by scabs I3 and 15. Hardwood blocks and balsa blocks are secured to the panels. At the edge portions of the panels defining the comer hardwood blocks 39 corresponding to blocks 21, are secured at distances from the line junction of the obtuse comer between the panels, corresponding to the spacings of the blocks 21 form the line junctionof a right-angled dihedral corner, so as to leave space S permitting slight deformation of the edge portions of the panels defining the corner.

Secured to the hardwood blocks 39 is an angle-section anchoring member 40 corresponding to the anchoring member 19 at the right-angle corner, but of the appropriate obtuse angle. Each limb of the member is secured to the blocks by bolts 20 engaged in captive nuts 25 in the blocks 39. In view of the spacings of the corrugations at the end of the elbow corrugation plates 37, the limb 40a of the anchoring member is somewhat longer than the limb 40b. The anchoring member 40 is provided with a reinforcing web 40c.

. FIG. 10 is a general perspective view of another membrane tank container 41 having an upwardly directed trunk 41a extending along its length and the sidewalls 41b of which container are stepped so that the vertical cross-sectional area of the container changes. The corners designated a are internal entrant corners whilst the corners b are external reentrant corners. At the corners a the arrangement of the anchoring members may be as described with reference to FIGS. 18. At the reentrant corners a somewhat similar arrangement will be adopted, for example that shown in FIG. 11.

In FIG. 11 the insulation is the same as in FIGS. 1-9, but the edge portions of the panels 8 constituting the reentrant corner of the insulationare reduced and rounded at 42 and the junction therebetween is covered by a scab 43 corresponding to scab 15. Hardwood blocks 44 corresponding to the blocks 21 (FIGS. 18) and 39 (FIG. 9)-are secured to the edge portions of panels 8 flanking the corner. The end of one block abuts against the side of the other block so that the two blocks together form a rigid right-angle structure. However, the rounded portions 42 of the panels 8 at the corner leave a space S (FIG. 11) between the panels and the blocks 44 to permit limited deformation of the panels 8 constituting the corner.

Secured to the hardwood blocks is a right-angle dihedral anchoring member 45, corresponding to member 19 (FIGS. 1- 8) similarly anchored by bolts 20 engaged in captive nuts 20a in the blocks 44. The member 45 is similar to the members l9 and has a reinforcing web 45c bu t is, in this example, of smaller dimensions, but could be of identical or larger dimensions, in order to be compatible with the spacing of the corrugations 16a, 16b of the sheets 16 forming the walls of the tank. Accordingly, each of the members 45 may be secured to each block by only two bolts 20. In all other respects the arrangement is identical with that described with reference to FIGS. l8.

The walls of the membrane tank defining the reentrant comer are connected by reentrant corner pieces 48, corresponding to entrant corner pieces 17, each having an elbow corrugation connecting the corrugations in the walls.

The member 45 adjacent each end wall, such as 16, is formed as a trihedral member with a large limb 50 in the plane of the wall 16. Welded to the limb 50 and to the adjacent membrane corner pieces 17 is a small flat sheet 49 forming part of the membrane.

FIG. 12 shows a modified form of dihedral anchoring member 46 corresponding to member 19. in this case, the member is of such thickness that it is sufficiently rigid, against angular deformation, within the required limits, that no webs are required. This simplifies the construction not only of the member but of the hardwood blocks 21 since no gaps need be provided between the blocks 21 and 23 (FIGS. 1-8) to accommodate the webs. Moreover, the hardwood blocks would, as shown in FIG. 9, be of the same length as the supporting corner pieces instead of being limited by the distance between the webs. Moreover, instead of being secured by screws passing through the block perpendicularly of the limb conthrough lugs 33.

We claim:

1. a. A generally prismatic container for cryogenic liquids such as liquid methane gas at substantially atmospheric pressure, comprising:

b. a primary barrier membrane tank having walls of flexible liquid-impervious material;

0. secondary tank walls of load-bearing thermal insulation,

each of said walls having a smooth, substantially continuous inner surface against which a wall of said membrane tank rests;

d. at least two of said secondary tank walls meeting each other at a corner;

e. rigid angle-section anchoring members each having two sides meeting at substantially the same angle as is formed by said corner, said sides being fixedly secured to said two secondary walls at said corner, said anchoring members extending along the full length of said corner, the inner surfaces of said members being substantially flush with the inner surfaces of said secondary walls;

. said angle-section sides being of sufficient tensile strength to transmit to said secondary walls the loads upon the anchoring members without any appreciable deformation; and

g. said membrane tank walls being firmly fixed at said corners to said anchoring members.

2. A container according to claim 1:

h. said membrane tank being fixed by said anchoring members, at all corners of the container. to the secondary tank walls.

3. A container according to claim 2:

i. and a rigid outer supporting shellfor said container, to which said load-bearing thermalinsulation is secured against movement away from the shell; and

j. said thermal insulation being of wood so that when subject to a change of temperature it does not deform except to a limited extent at the corners so that it permanently provides a smooth supporting surface for the membrane tank.

4. A container according to claim 3:

k. and fastening means securing each said anchoring member to the insulation adjacent the line junction of the respective corners of the load-bearing insulation walls so as not to interfere with deformation of such corners under expansion and contraction of the insulation.

5. A container according to claim 4:

1. said fastening means including rigid load-bearing insulation blocks of material such as hardwood rigidly secured to said insulation wall;

rn. said blocks extending along each wall portion flanking the corner line junctions, but leaving a gap between the fastening means and said line junctions to accommodate any corner deformation.

6. A container according to claim 5, and outer fastening means between said insulation walls and the walls of said shell such that part of the tensile load in any wall of the membrane is taken in shear through said wall of insulation to that wall of the shell extending parallel to said wall ofthe membrane. 

